PYRIDINE-TYPE COMPLEXES OF TRANSITION-METAL HALIDES .3. STRUCTURAL AND THERMAL RELATIONSHIPS AMONG THE COBALT(II) COMPLEXES WITH HALIDE-IONS AND 2-METHYLPYRIDINE, 3-METHYLPYRIDINE, AND 4-METHYLPYRIDINE, THE CRYSTAL-STRUCTURE OF DIBROMOTETRAKIS (3-METHYLPYRIDINE)COBALT(II)

The correlation between structure and thermal properties of halogeno m ethylpyridine cobalt(II) is described. The ternary mixed tetrakis-deri vatives and the tetrahedral bis-complexes of cobalt(II) chlorides and bromides formed with picolines are structurally very similar to the ca dmium(II) and nickel(II) analogues; the iodides are somewhat different , however. On the basis of the characteristic correlation between the densities calculated from powder diffraction data and the molecular we ights, the densities of a few thermal intermediates, which have not ye t been prepared, are predicted. The square bipyramidal structure of di bromotetrakis(3-methylpyridine)cobalt(II) is described, and the deform ation of the octahedra is discussed in detail. Structural study was ex tended by molecular mechanics (MM+ and MMX) and molecular orbital (SIN DO1) calculations.